1. Field of the Invention
This invention relates to a substrate holding device. In particular, this invention relates to a wafer holding device provided with a rotatable plate pivoted with jaws to effectively clamp a wafer thereon by means of centrifugal force.
2. Description of Prior Art
Referring to FIG. 1, a side view depicts the structure of a wafer W rotated by a wafer holding device 1 to perform the cleaning process according to the prior art.
As shown in FIG. 1, the wafer holding device 1 comprises a base 10, a vacuum pump 12 and a motor M. The base 10 is a supporting plate used to support wafer W and is rotated above an axis A--A by the motor M. A sucking portion 100 formed on the top surface of the base 10 is a concavity communicated to the vacuum pump 12 by a channel 13. Wafer W is placed on the sucking portion 100 of the base 10 and sucked by the vacuum pump 12 and rotated with the base 10 above the axis A--A. Given the acting force of the flushing water during the cleaning, the contact and suction between the wafer W and the base 10 must be well maintained to prevent disengagement of the wafer W during the rotation.
FIG. 2A is top view of a wafer holding device 2 according to the second prior art, and FIG. 2B is front view showing the structure of the wafer holding device 2 according to FIG. 2A. As shown in FIG. 2B, the holding device 2 of a second example of the prior art comprises a rotatable base 20, a plurality of pins 21 used to support the wafer W and a motor M used to actuate the base 20. The pins 21 are spaced apart from each other and mounted on the upper surface of the base 20, symmetrically and vertically. Each of the pins 21 is provided with a step portion 210 composed of surfaces 211, 212 and the wafer W is limited and clamped therebetween. The fit and clearance of the wafer W set between the pins 21 should be accurately calculated, otherwise the wafer W easily disengages from the pins 21 when the base 20 is rotated above the axis A--A at a high speed.